class_docstr: Class for optimized implementation of Backdoor variable search between the source nodes and the target nodes.
code: def __init__(self, graph, nodes1, nodes2):
      self._graph = graph
      self._nodes1 = nodes1
      self._nodes2 = nodes2
      self._nodes12 = set(self._nodes1).union(
          self._nodes2
      )  # Total set of nodes
      self._colliders = set()
  
imports: import networkx
  from dowhy.utils.graph_operations import adjacency_matrix_to_adjacency_list
label_desc: Use image node_id 1 to create a new Backdoor object  with example: obj = Backdoor(graph, nodes1, nodes2)